1. 1x Wireless-Communication Networks Generally
Many people use wireless-communication devices, such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These wireless-communication devices and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1 xRTT networks” (or “1x networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Wireless-communication devices typically conduct these wireless communications with one or more base transceiver stations (BTSs), each of which sends communications to and receive communications from wireless-communication devices over the air interface. Each BTS is in turn communicatively connected with an entity known as a base station controller (BSC), which (i) controls one or more BTSs and (ii) acts as a conduit between the BTS(s) and one or more switches or gateways, such as a mobile switching center (MSC) and/or packet data serving node (PDSN), which may in turn interface with one or more signaling and/or transport networks.
Wireless-communication devices and base stations conduct communication sessions (e.g. voice calls and data sessions) over frequencies known as carriers, each of which may actually be a pair of frequencies, with the base station transmitting to the wireless-communication device on one of the frequencies, and the wireless-communication device transmitting to the base station on the other. The base-station-to-mobile-station link is known as the forward link, while the mobile-station-to-base-station link is known as the reverse link.
Wireless-communication devices can typically communicate with one or more endpoints over the one or more signaling and/or transport networks from inside one or more coverage areas (such as cells and/or sectors) of one or more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typical arrangements, MSCs interface with the public switched telephone network (PSTN), while PDSNs interface with one or more core packet-data networks and/or the Internet.
2. Pilot Channels and Traffic Channels Generally
Using a sector as an example of a coverage area, BTSs may provide service in a given sector on one carrier, or on more than one. An instance of a particular carrier in a particular sector is referred to herein as a sector/carrier. In a typical CDMA system, using a configuration known as radio configuration 3 (RC3), a BTS can, on a given sector/carrier, transmit forward-link data on a maximum of 64 distinct channels at any time, each corresponding to a unique 64-bit code known as a Walsh code. Of these channels, typically, 61 of them are available as traffic channels (for user data), while the other 3 are reserved for administrative channels known as the pilot, paging, and sync channels.
When a BTS instructs a wireless-communication device that is operating on a given sector/carrier to use a particular traffic channel for a communication session, the BTS does so by instructing the wireless-communication device to tune to one of the 61 traffic channels on that sector/carrier. It is over that assigned traffic channel that the BTS will transmit forward-link data to the wireless-communication device during the ensuing communication session. In addition to that forward-link channel, the traffic channel also includes a corresponding Walsh-coded reverse-link channel, over which the wireless-communication device transmits data to the BTS.
The BTS also continuously transmits on the pilot channel a pilot signal that can be picked up by nearby wireless-communication devices. In general, the pilot channel functions to alert wireless-communication devices in a given sector of the presence of a service-providing BTS. Typically, the pilot channel also conveys a value known as a pseudorandom number (PN) offset, which identifies the sector; in particular, by being offset from CDMA system time by a certain amount of time, the pilot channel conveys the PN offset. Wireless-communication devices generally use the pilot channel to coherently detect and demodulate, or decode, the signal on a sector/carrier, including communications sent on the traffic channel.
3. Pilot and Traffic Signal Transmission Power
Typically, the power level at which the pilot signal is transmitted is at least as high as the power at which signals on any other channel are transmitted, including the traffic signals. The pilot-signal power level is typically fixed at a certain level, and the pilot-signal power level therefore typically serves as a maximum transmit power for signals transmitted on all other channels. Conversely, the power level at which the traffic signals are transmitted may vary in time depending on a variety of considerations, including forward-link RF conditions.
Wireless-communication devices typically continuously compute a forward-link frame error rate (FFER) which is a ratio of the number of error-containing frames that the wireless-communication device receives to the total number of frames that the wireless-communication device receives over a given period of time. If the FFER exceeds a desirable amount, a wireless-communication device might report that fact to the BTS, and the BTS will then increase the forward-link transmission power to the wireless-communication device on the traffic channel. Other things being more or less equal, the more power that the base station allocates to a given wireless-communication device, the lower the wireless-communication device's FFER will be.
Nonetheless, a wireless-communication device typically is not allowed to request an increase in the BTS transmit power of the traffic signal to a level that is greater than the transmit power of the pilot signal. As one practical consideration, increasing the power at which the traffic signal is transmitted would normally be ineffective without correspondingly increasing the power at which the pilot signal is transmitted such that the wireless-communication device would also be able to receive the pilot signal for decoding the traffic signal. Accordingly, it is generally understood that the power level of the pilot signal, and its associated geographic reach, corresponds to the limit of the coverage area for a given BTS.